Although millions of lives have been saved by new biomedical technologies and expansion of prevention and treatment in low- and middle-income countries, many vulnerable people ? including in the US ? are not benefiting from these advances. Implementation science (IS) research can maximize public health impact by addressing suboptimal implementation of evidence-based strategies; identifying ways in which health care systems and policies fail to adequately address the HIV prevention and care continua; and identifying population-based strategies to improve HIV outcomes in the US and globally. The Implementation Science and Health Outcomes (ISHO) Core will address the HIV Center's overall theme by catalyzing innovative IS research that identifies and tests strategies to optimize ?real-world? uptake and impact of effective HIV prevention and care continua interventions at scale. The Core has three Specific Aims: (1) to stimulate new IS research and collaborations to improve key outcomes along the HIV prevention and care continua; (2) to advance new IS research to prevent or reduce HIV-related health disparities that are driven by suboptimal intervention implementation or by psychiatric and other comorbidities; and (3) to promote the use of health policy analysis, policy modeling, and economic evaluation to bridge the evidence-practice and evidence-policy gaps that drive suboptimal population-based implementation and disparities. The ISHO Core will accomplish its Aims through functions that include (1) providing expert consultation to HIV Center researchers on conducting IS research that (a) both tests new approaches to improve HIV-related programmatic outcomes and assesses causes of successful and un-successful implementation of interventions and policies at scale, and (b) incorporates the perspectives of policy translation, policy modeling, and economic evaluation into their research; (2) developing Scientific Working Groups to provide structured and focused guidance to (and collaboration with) Center investigators interested in or embarking on IS through dynamic small groups organized around specific themes (e.g., PrEP implementation, psychiatric comorbidities); (3) facilitating access to linked networks for HIV Center investigators addressing IS-related research questions; and (4) sponsoring seminars to stimulate the use of IS approaches in research. The proposed Core Director, Denis Nash, Ph.D., is an epidemiologist and Director of the Institute for Implementation Science in Population Health (ISPH) at the City University of New York. Core Co-Director, Milton Wainberg, M.D., is a research psychiatrist at the New York State Psychiatric Institute and Columbia University Department of Psychiatry. Together they have extensive expertise in NIH-funded research and capacity building for HIV and mental health treatment and prevention. The Core brings together early stage, mid-career, and established investigators in the areas of IS, health-disparities, and economic evaluation with policy-makers and program implementers to provide an infrastructure for research collaboration.